Initial studies here suggest that asbestos induces DNA degradation in cultured normal human fibroblasts, and that DNA degradation is detectable in viable cells at concentrations as low as 1 particle per cell. DNA degradation may be involved in the previously-reported ability of asbestos to induce chromosome aberrations and mutation in vitro. Because large numbers of people have been exposed to asbestos and exposure has been linked to an increased risk to pleural and peritoneal mesotheliomata, the elucidation of the mechanism of action of asbestos on the genetic material of the human cell warranted. The purpose of this proposal is to further our initial observations in effort to learn about the effects of asbestos on the DNA, chromatin, and chromosomes of human cells. DNA degradation induced by fibers of different composition and size will be correlated with their known toxic and carcinogenic properties. Whether asbestos-induced DNA degradation is restricted to only a portion of the genome or widely distributed throughout the DNA will be revealed by DNA sedimentation in alkaline sucrose gradients. The release of lysosomal enzymes and radiolabel from DNA will be correlated kinetically with the formation of single-strand breaks in DNA detected by alkaline elution. This will help put in perspective the course of events which occur after asbestos is phagoxytized. The chemical nature of the DNA degradation products released into the medium will be studied to determine whether specific or random degradation products are formed, and to contribute to an understanding of the possible mechanism by which asbestos induces degradation. The effect of asbestos on chromatin will be examined with respect to the alteration of its chemical composition, the ratio of histone to nonhistone proteins, the proportion of protein in the different histone classes revealed by disc electrophoresis, and the degree to which chromatin is nuclease sensitive. The involvment of DNA repair in asbestos-induced degradation will be examined by the ability of asbestos to induce unscheduled DNA synthesis, the sensitivity to asbestos of human cells which are presumed mutants for DNA repair or derived from patients prone to malignancy, and the accumalation of DNA strand breaks in cells treated concurrently with asbestos and proflavin. Whether lysosomal enzymes are responsible for the observed DNA degradation will be assessed from the effects of the inhibition of lysosomal enzymes with chlorquine and lysosomal fusion with Colcemid on the elutability of DNA (strand break formation). Cells with genetic defects in lysosomal enzymes or function will be similarly examined. The types and distribution of lesions with respect to particular chromosomes and regions of chromosomes will be determined from preparations of banded mitotic chromosomes.